The present invention relates to an optical communication module, mounted on the end face of an optical fiber, for receiving an optical signal transmitted via the optical fiber and transmitting an optical signal via the optical fiber.
In a conventional optical communication system by bidirectional transmission using light having different wavelengths, an optical communication module containing an optical system composed of a light receiving device, light emitting device and lens is mounted on a terminal by which a light signal is transmitted and received through an optical fiber. Using the diffraction effect by diffraction structure, the optical system of such an optical communication module separates the transmitted light from received light, whereby the image of the transmitted light from the light emitting device is formed on the optical fiber and the received light from the optical fiber is received on the light receiving device. This arrangement provides smaller size and cost reduction.
In the optical system of the conventional optical communication module disclosed in Patent Document 1, a diffraction structure is formed on one of the optical surfaces of the optical element. The transmitted light emitted from the light emitting device is allowed to pass by, without being diffracted by the diffraction structure, and reaches the end face of the optical fiber. The luminous flux emitted from the optical fiber is provided with diffraction effect by the diffraction structure so that the direction of emission is changed, and the luminous flux enters the light receiving device.
[Patent Document 1] Tokkai 2003-344715
In the optical communication module disclosed in the Patent Document 1, there is agreement between the axis of the optical fiber and the optical axis of the optical element. The transmitted light is applied in the direction perpendicular to the optical surface provided with the diffraction structure of the optical element, and the received light is emitted so as to form an angle from the optical surface provided with the diffraction structure. In such a structure, however, when the received light is emitted in the form provided with an angle by the diffraction structure, part of light may be cut off by the stepwise diffraction structure and the light transmittance may be reduced. Reduction of light transmittance may produce an error signal. Further, the end face of the optical fiber is tilted at a predetermined angle so that light reflected therefrom is not travel backward. The received light emitted from the end face of the optical fiber is tilted with respect to the axis of the optical fiber. This raises the problem of how to handle the relationship between the tilt and diffracted angle. Further, the diffraction structure is a microstructure, and therefore, its high-precision formation on the optical surface is difficult. Moreover, there is a requirement for further reducing the deterioration of the aberration of the light having passed through the optical element.